Electrocatalytic CO2 reduction to HCO2H by protic NHC-Ir complexes

In electrochemical CO₂-conversion strategies, various transition metal-based molecular electrocatalysts are employed to reduce CO₂ into products like CO and HCO₂H, with H₂ as a competitive side product. However, achieving selectivity towards HCO₂H remains challenging, and suitable catalysts for the same are limited. Herein we report a normal and an abnormal protic-NHC-based Cp*Ir(III)-half sandwich complexes for catalytic CO₂ electroreduction in an aqueous acetonitrile solvent. Both the catalysts predominantly produced HCO₂H as the CO₂-reduced product at an applied potential of –2.66 V vs Fc⁺/Fc with 5 % H₂O as the proton source; however, the normal protic-NHC-bound complex achieved a Faradic efficiency (FE) of 86±4 %, while the complex with the abnormal protic-NHC ligand furnished FE up to 72±4 %. The protic proton of the protic NHC ligand in these complexes was proposed to participate in a proton relay process, facilitating generation of the crucial Ir–H intermediate, which reacts with CO₂ to produce HCO₂H through stabilization of the Ir–OCHO intermediate.